1. Field of the Invention
The present invention relates to an ink composition for manufacturing color filters, and more particularly, to an ink composition having good chemical resistance and adhesive properties and used for manufacturing color filters exhibiting high contrast ratios.
2. Description of the Related Art
In related art photolithography methods used for manufacturing color filters or black matrices, the resulting color filters exhibit good properties in terms of elaborateness and reproducibility. However, to form pixels, photosensitive compositions including pigments of three primary colors, respectively, should be subject to each process of coating, exposing, developing and curing. This gives rise to problems in that a manufacturing line may be overly lengthened; it becomes difficult to control production yield due to an increase in process-controlling factors; and a thick coating layer is required for high color reproducibility.
To solve these problems, an inkjet method has been proposed, wherein a desired pattern is formed by directly printing a liquid ink on a substrate using an inkjet head.
In the inkjet method, inks including pigments (R, G and B) of three primary colors are sprayed on a substrate, and image regions with each ink colored form pixels having desired patterns. Thus, since a manufacturing process is even simpler than that of related art photolithography methods, and also, as manufacturing costs are relatively low compared to those of related art photolithography methods, the inkjet method is now widely used as a method for manufacturing color filters.
However, a color filter manufacturing process is exposed to lots of chemicals, and therefore, a color filter should have chemical resistance for enduring this process even after the color filter is formed. In particular, an oriented film is coated during a process subsequent to the color filter forming process, and a main solvent of an oriented film material used during this process is NMP. Therefore, when the color filter thus formed is exposed to NMP, it is preferable that resistance to NMP is evaluated and evaluation results are used as an index for chemical resistance in order to prevent pigments from being eluted, swollen and peeled.
As described above, inks which are sprayed on the substrate to form patterned pixels should have high chemical resistance and adhesive properties. If the chemical resistance is insufficient, some pigments contained in the ink may be eluted into a solvent. If the adhesive properties are insufficient, some of the colored ink may be peeled after a heat treatment process. The pigments thus eluted or peeled may cause fatal failure in the manufacturing of LCD panels.
In particular, the recent trend of color filter development requires high color reproducibility and brightness, and pigments should be highly concentrated and atomized. To this end, the content of pigments in an ink composition for manufacturing color filters is increased to give a darker color at the same thickness. However, as the content of pigment increases, the content of other components such as a cross-linking agent, a binder, and resin is relatively reduced. As a result, such changes in contents may cause an ink-coated film to lack sufficient strength, thereby leading to printing failure and a decrease in chemical resistance.